This invention relates generally to adjuster mechanisms, and in particular to a headlamp adjuster mechanism for use in motor vehicles.
As the design of vehicles, automobiles and small trucks in particular, has evolved, headlights have continually been reconfigured to improve the aerodynamics of the front end of the vehicle. Modern headlights are designed so that their lenses follow the contour of the vehicle to provide an aerodynamically efficient exterior surface. However, adjustment of these headlights must still be performed in order to provide an optimal beam of light and to prevent the aiming of light beams toward oncoming vehicles. Automotive manufacturers' demand for aerodynamically efficient headlight designs has lead to modular designs requiring the headlight adjustment mechanism to be located within the interior of the engine compartment so that adjustment can be easily performed without removing any trim pieces. Thus, the constraints of the installation area and the demands of the automobile manufacturers for aerodynamic headlight designs dictate that an adjuster for use with the aerodynamic designs be adjustable from inside the engine compartment using ordinary tools, and must be able to translate rotational motion of the adjusting part into linear motion of the adjusting means that adjusts the lamp within the headlight assembly. There are many devices incorporating such designs including, among others, the devices disclosed in U.S. Pat. Nos. 5,707,133 and 5,214,971 to Burton, the inventor of the present invention, the disclosures of which are incorporated herein by reference.
Automotive lamp assemblies used as headlights typically include several basic parts: a support frame, a reflector, a lens, a bulb, and one or more adjusters. The support frame either completely houses the reflector and the bulb on a pivotable mounting to allow the aim of the light to be adjusted using the adjusters or provides a mounting surface for attaching a headlamp adjuster. The lens seals the front of either the support frame or directly to the reflector to protect it from the elements assailing the front end of the vehicle and provides an aerodynamic shape and attractive appearance. The reflector mounts on one fixed ball joint and is adjustable horizontally and vertically using adjusters that interface with the reflector through moving ball joints. The moving ball joints are moveable by actuating the adjusters connected to the moving ball joints by a ball stud having a head and a shaft. Right angle style adjusters, such as the ones disclosed in the referenced Burton patents, are often used to allow the adjustment of the headlight from an adjusting position above the installed headlight. In other applications, motorized adjusters, straight adjusters, or other types of adjuster are used.
One illustrative example of a conventional right angle style headlamp adjuster design is U.S. Pat. No. 4,939,945 to Ryder et al. which discloses a headlamp adjuster having a housing member with two internal chambers--a drive gear chamber and an adjustment gear chamber. The drive gear chamber contains a bevel drive gear and intersects the adjustment gear chamber containing a bevel adjustment gear. Each chamber is dimensioned to position the gears such that they intermesh to translate a rotation of the drive gear into a rotation of the adjustment gear. Such a rotation of the adjustment gear translates into linear movement of a rotationally restrained threaded adjustment member which ultimately causes a change in the angle of the lamp within the headlamp assembly. Rotation of the adjustment member is restrained by the non-rotatable attachment of the adjustment member to the reflector of the headlamp. The adjustment gear includes an adjustment gear bore that is formed through the center of the adjustment gear to engage the adjustment member projecting therethrough. The adjustment gear bore is shaped such that when a thread forming adjustment member is threaded therethrough, the plastic material which is displaced by the threads on the adjustment member has areas in which to flow and threads are formed. Alternatively, the adjustment gear bore is formed with interference threads that mate with threads on the adjustment member. In either embodiment, the interference between the adjustment gear bore and the adjustment member provides a prevailing torque tending to retain the adjustment member in the desired adjustment by providing rotational resistance.
There are a number of drawbacks to headlamp adjuster designs such as the one disclosed in the Ryder et al. patent. First, it is difficult to control the amount of prevailing torque that retains the adjustment member in the desired adjustment. This difficulty arises from the interference or thread-forming fit between the adjustment gear bore and the adjustment member because it is difficult to consistently control the amount of interference due to narrow machining and assembly tolerances. Furthermore, there are many variables to control and influence the prevailing torque variation, e.g., gear tooth profile, gear alignment, gear forces and surface friction between the other moving parts in the gear box. Additionally, if a thread-forming method such as the one disclosed in Ryder et al. is used, small chips of material may be created which tend to impede the rotation of the adjustment gear around the adjustment member.
Second, assembly of the thread-forming adjustment member into the adjustment gear is somewhat problematic. This is because thread-forming has constraints with regard to driver speed during assembly. If the driver speed is too fast, the plastic adjustment gear could significantly soften or melt during driving which can result in a poor quality assembly and/or damage to the internal thread. Restricting the driver speed can slow down the assembly process resulting in added assembly cost. Additionally, precise driving of the adjustment member into the adjustment gear is required to ensure proper orientation of the adjustment shaft within the adjustment gear and to prevent damage to the adjustment gear during assembly. This complicates automated assembly.
Third, conventional adjusters such as the one disclosed in Ryder et al. can cause damage to the reflector or can themselves fail if the input shaft is continued to be rotated beyond the adjustment shaft's designed range of travel. Damage occurs if the adjuster is over-adjusted in either direction to the point where the adjustment member forces the reflector to the point of cracking or breaking or the force between the adjuster, the reflector, and the housing is such that the adjuster itself becomes dislodged or otherwise misaligned or has an internal failure.
The mechanical advantage gained by using a threaded adjustment shaft produces high levels of force with minimal applied adjustment torque. This mechanical advantage combined with the inherent variations in prevailing torque hinders the recognition of potentially damaging torque build-up before damage or failure occurs. Attempts have been made to design an input shaft assembly that has a torque-limiting feature that slips under excess torque build-up from over-adjustment. However, such input shaft systems often prematurely slip and prevent desired adjustment because the mechanical advantage of the thread causes the variations related to prevailing torque and input shaft torque limiting variation to overlap.
Accordingly, a need exists for a headlamp adjuster in which the rotation resistance can be more precisely controlled, which has a smooth operation, which prevents damage-causing adjustments or over-adjustments, and which is cost-effective and easily manufactured and installed.